Marco's Tech Blog
– Up to Delphi 102, if you used a custom attribute that was not known to the compiler (because you typed it incorrectly or a unit was missing in the uses statement), you'd receive the warning: Warning: W1025 Unsupported language feature: 'custom attribute' This message was misleading, because the feature has been in the language for quite some time, it was just using an undefined symbol in it. There is a large list of reports on this issue, including https://quality.embarcadero.com/browse/RSP-20384. Starting with 10.3, the same code will trigger a new specific warning: ...